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MVP view
AppController: which page to go next.
View: create UI.
Presenter: show content.
Display:

main application start
controller created with Event Bus
RootPanel passed to controller.
History.onValueChange is invoked. (in controller)
Base on value of history token, a presenter is created with corresponding concrete View class. View class define UI for the page.  (in controller) 
Presenter setup event handling and other actions for page. And call View.asWidget() (in presenter)

Roles:
Presenters - always have an instance of EventBus, and can fire event that can direct navigation of pages.


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